Foods That Cause Protein in Urine medically known as proteinuria, is a condition where excess protein leaks into the urine instead of staying in the blood. Normally, kidneys filter waste while retaining essential nutrients like protein. When the kidneys are stressed or damaged, protein can pass into urine. While medical conditions such as diabetes, high blood pressure, or kidney disease are common causes, diet also plays an important role. Certain foods can worsen kidney strain and may contribute to protein in urine, especially when consumed regularly or in excess.